Propeller blade pitch is defined as the distance that a propeller would move in one revolution if it were traveling through a soft solid, like a screw in wood, "Everything You Need To Know About Propellers", Third Edition, Mercury Marine Division of Brunswick Corporation, Catalog QS5-384-10M, Part No. 90-86144, page 6, and FIG. 8, page 7. For example, a propeller with a twenty-one inch blade pitch would move forward twenty-one inches in one revolution, a propeller with a ten inch blade pitch would move forward ten inches in one revolution, and so on. Optimum pitch is determined by various factors, including load, speed and boat type. For example, when propelling a boat from rest and for a heavy load, such as towing a water skier, a low pitch propeller is desired. On the other hand, at higher speeds, a high pitch propeller is desired. In the majority of marine propulsion systems, a single pitch propeller is used, and the pitch is selected as a trade-off between the above noted opposing factors.
Variable pitch marine propellers are known in the art. The propeller includes a hub rotatable about a longitudinal axis and having a plurality of blades extending radially outwardly therefrom and pivotable about respective radial pivot axes between a low pitch position and a high pitch position. The blades are initially in the low pitch position for start-up acceleration, and then pivot to the high pitch position at higher speed, for example Bergeron U.S. Pat. Nos. 4,792,279 and 5,022,820 and Speer U.S. Pat. No. 4,929,153. Prior propellers typically use increasing centrifugal force with increasing rotational speed of the propeller to pivot the blades to an up-pitched position, and some propellers use a positive locking mechanism to prevent the shift until a designated threshold centrifugal force is reached.